The present invention generally relates to power tools that have a table that is rotatable on a base, and more particularly to a locking assembly for locking the table.
Power miter saws have long been used to cut work pieces such as trim, molding and the like where precise angled cuts are made. Such miter saws generally have a base on which a rotatable table is mounted, the table being adjustable around a center pivot axis. A user can adjust the angle of the table relative to a fence, and a blade and motor assembly is generally attached to the table and can be lowered into a cutting position. It is common for the table to have angular indicia so that a user can quickly rotate the table to a desired angular position so that cuts can be made.
Such miter saws have detents for commonly used angular positions such as 22½°, 45°, as well as others, and also have locking mechanisms for locking the table in a preferred predetermined position.
All known miter saw locks have at least one of three undesirable characteristics. First, locking the miter angle can cause the table itself to bend, which can detrimentally affect the accuracy of miter cuts made by the saw. Second, locking the table can cause the preset miter angle to move, which can also affect the accuracy of the cut. Third, locking the table may cause the top surface of the table to go out of plane relative to the base. Any one of the three characteristics can have an adverse effect on the quality of the cuts made by the miter saw.
With regard to the characteristic of the table bending, the location of the opposing forces that are produced during the locking action is the main cause of this. Moving the locking mechanism components closer to one another by reducing the span on the table can effectively reduce this characteristic. With regard to the miter angle movement, it is a common characteristic of many locking mechanisms to lock the miter angle by turning the screw against a stationary wall. This can cause the miter angle to move as the screw tightens. Tightening the lock knob will generally cause the table to rotate slightly in the counterclockwise direction, which can detrimentally affect precision cuts. An acceptable solution to overcome this characteristic is to have the screw tighten against an intermediate piece, which is effective if the piece is not allowed to rotate. Other designs have addressed this problem by using linkages and cams instead of screws to lock the miter angle.
With regard to the out of plane table movement, there are no known locking assemblies that effectively address this problem or characteristic. All known miter lock designs utilize the pivot point of the table to the base to provide the opposing force when the miter locking assembly is engaged. For a freely moving pivot connection, there must be clearances in the pivot joint. When the miter lock assembly is engaged, the pivot joint is pushed to one side of the clearance, and that causes the table to move out of plane, relative to the base.